This invention relates generally to printers, and more particularly, although not exclusively, to inkjet printers.
It is generally known that inkjet printers utilize black pigment based inks to print text and line drawings. This is due to pigment based inks being relatively more opaque and lightfast than dye based inks. However, dye based inks are particularly suited to the production of color images. In this regard, conventional printers designed to print both text and color images may utilize a black pigment based ink and a set of dye based inks (e.g., cyan, yellow and magenta). For example, U.S. Pat. No. 5,745,140, assigned to the HEWLETT-PACKARD COMPANY, discloses a color inkjet printer with pigment black and dye based color inks and the disclosure of which is hereby incorporated by reference in its entirety.
While black pigment based ink is generally regarded as being superior to black dye based ink for text and line drawing, conventional black pigment based ink does have a number of disadvantages. Specifically, conventional black pigment based ink has a greater capacity to clog the printhead nozzles. In an effort to reduce the effects of decap (e.g., clogged nozzles, pigment migration, etc.), a multitude of patents have disclosed various manner of improvements. For example, inks with extended drying times have been developed. However, slow drying inks generally produce higher levels of image quality defects associated with so-called xe2x80x9cbleedxe2x80x9d. Bleed is a term of art used to describe excessive spreading of an ink on a print medium as well as the infiltration of one color into another on the print medium. In this regard, U.S. Pat. No. 6,086,198, assigned to the HEWLETT-PACKARD COMPANY, discloses a set of inks for reducing or eliminating color bleed, the disclosure of which is hereby incorporated by reference in its entirety.
Additionally, while pigment based ink is relatively more opaque than dye based ink, to ensure highly opaque black regions, various conventional printing systems have been developed to xe2x80x9cfortifyxe2x80x9d black printed areas. Some of these fortification methods have the added benefit of reducing the drying time by utilizing an interaction between the dye based and pigment based inks. For example, it is generally known to use dye based cyan and magenta (colored) inks as a fortification for pigmented black ink. The colored inks are deposited on the print medium and the black ink is subsequently deposited over the colored inks. The colored inks and the black ink may interact. Thus producing a more opaque black that dries relatively faster and bleeds relatively less. However, to reduce the possibility of the colored inks being visible around the edges of the black region, the colored inks are not deposited around the edges of the black region. Due to the lack of fortification about the edges of black regions, color fortification of black regions may not adequately conceal defects associated with decap. Furthermore, hue shift defects (e.g., purple tones) are often evident in regions of color fortification.
In one respect, the invention pertains to a method of improving the print quality of a print job having black content. The black content has a predetermined location on a print medium. In the method, the black content is fortified by applying a black dye based ink on the predetermined location and the black content is printed by applying a black pigment based ink on the predetermined location.
In another respect, the invention pertains to an apparatus for improving the print quality of a print job having black content. The black content has a predetermined location on a print medium. The apparatus includes a first printhead configured to fire black dye based ink droplets on the print medium, a second printhead configured to fire black pigment based ink droplets on the print medium and a processing system configured to fortify the black content by controlling the first printhead to fire droplets on the predetermined location. The processing system is further configured to print the black content by controlling the second printhead to fire droplets on the predetermined location.
In comparison to known prior art, certain embodiments of the invention are capable of achieving certain aspects, including some or all of the following: (1) elimination of hue shift defects associated with color fortification of black pigment based ink; (2) improving throughput via the removal of fortification firmware; (3) reducing defects associated with decap and (4) improving image quality on glossy print medium. Those skilled in the art will appreciate these and other aspects of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings.